docs: def fake(cls, gsimlt=None):
          """
          :returns:
              a fake `CompositionInfo` instance with the given gsim logic tree
              object; if None, builds automatically a fake gsim logic tree
          """
          weight = 1
          gsim_lt = gsimlt or logictree.GsimLogicTree.from_('[FromFile]')
          fakeSM = logictree.LtSourceModel(
              'scenario', weight,  'b1',
              [sourceconverter.SourceGroup('*', eff_ruptures=1)],
              gsim_lt.get_num_paths(), ordinal=0, samples=1)
          return cls(gsim_lt, seed=0, num_samples=0, source_models=[fakeSM],
                     totweight=0)